Certain refractory powders, used to form refractory shapes by compressing the powders at an elevated temperature, can be produced by reaction of metal oxides with carbon to form carbides, or borides if a boron source is also added. Such processes are disclosed in, for example U.S. Pat. Nos. 3,351,428, 2,906,605, 2,973,247, 3,004,830, 3,013,862, 3,246,956, and 3,328,127.
For some applications, an alloyed refractory shape is desired, e.g. a shape of titanium boride and chromium diboride. Typically these alloyed refractory shapes are formed by blending different powders together, with a powder for each component, and then hot-pressing the blended mixture. A problem with these processes, is that, even with extensive blending, the uniform distribution of the different powders is difficult to achieve. In addition, each powder must be prepared separately, which results in a substantial increase in the number of process steps required to form the refractory shape.
In addition to blended powders for alloys, mixed powder compositions are often produced to introduce sintering aids, and other process aids, into the powders. Certain refractory powders, such as those of titanium diboride and boron carbide, cannot be hot-pressed or sintered in their pure form to form a product of sufficient density and strength. In order to form suitably dense and strong refractory shapes from these powders, a small amount of sintering aid is required. For example, titanium diboride powders used commercially usually contain iron, nickel, and/or cobalt, which act as sintering aids. Generally, these sintering aids are introduced into the powder by ball milling the powders with stainless-steel or tungsten carbide balls (which generally contain 6 to 12 wt. % cobalt) through attrition of the balls. Alternately, sintering aids, such as the above metals, nickel diboride, or chromium diboride, can be added to the refractory powder and the mixture blended before hot-pressing of the powder. A problem with these methods, is that it is difficult to obtain a uniform distribution of the sintering aid in the powder. In addition, in methods which rely upon attrition of the milling balls to add the sintering aid, it is difficult to control the amount of sintering aid added to the powder.